The revelation came as the company reported a huge increase in half-yearly profits. In the six months to September, their profits rose to £144million, compared with £12million in the same period last year.

The Royal Mail have argued marketing mail helps drive commerce

Chief executive Moya Greene admitted "direct marketing" was approaching 50 per cent of all deliveries - and she also warned: "We are poised to increase our share of it."

She said Royal Mail was climbing out of a "very deep hole" with all parts of the business now profitable.

Ms Greene added: "I believe our people generally understand the need for the company to continue to adapt to a rapidly changing postal market and that the company and the unions need to work together for the benefit of both our customers and our colleagues."

Clyde Loakes, of the Local Government Association, claimed he had raised previously concerns about the increase in unsolicited mail.

He said: "Not only is it a nuisance to have to pick up and throw away but it adds thousands of tons to the amount of waste councils have to collect."

Robert Hammond, of the campaign group Consumer Focus, said that while direct marketing was frustrating it does help keep down the price of postage.

He added: "The hard fact is that without this revenue stream for Royal Mail and the associated profits, customers could, in fact, face paying more for their stamps."